JP2019094907A - Turbomachine - Google Patents

Abstract

To provide a turbomachine having good vibration characteristics.SOLUTION: A turbomachine (100a) of the invention includes a rotary shaft (4), a first disc wheel (3a), a first bearing (1) and a second bearing (2). The first disc wheel (3a) is fixed to the rotary shaft (4) and includes a lower pressure surface (31) which is subjected to relatively low pressure by a working fluid when the rotary shaft (4) rotates. The first bearing (1) is disposed at the lower pressure surface (31) side of the first disc wheel and supports the rotary shaft (4). The second bearing (2) is disposed so as to sandwich the first disc wheel (3a) with the first bearing (1) and supports the rotary shaft (4). The rotary shaft (4) includes a first taper part (41) having a diameter expanding toward the first disc wheel (3a). The first bearing (1) has a first support surface (11) for supporting the first taper part (41).SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a turbomachine.

  Conventionally, turbomachines are individually provided with a thrust bearing that supports an axial load (thrust load) associated with a differential pressure generated on both sides of a impeller, and a radial bearing that supports a radial load (radial load). . Turbomachines may also include angular contact ball bearings that support thrust and radial loads. Moreover, a tapered bearing is known as a bearing of a rotating shaft.

  Patent Literature 1 describes a turbocharger 300 including a turbine 302, a rotating shaft 303, a compressor wheel 304, a collar 306, a bearing 307a, and a bearing 307b, as shown in FIG. The rotating shaft 303 is formed with a tapered portion 305 whose diameter gradually increases from the middle portion of the rotating shaft 303 to the turbine 302 side. The collar 306 has a tapered shape whose diameter gradually increases from the middle portion of the rotating shaft 303 toward the compressor wheel 304. The collar 306 is fixed to the rotating shaft 303. The bearing 307 a is a tapered bearing having a diameter slightly larger than that of the tapered portion 305 corresponding to the tapered portion 305. The bearing 307 b is a tapered bearing slightly larger in diameter than the collar 306 corresponding to the collar 306.

  The bearing 307a and the bearing 307b are static pressure gas bearings. Compressed gas is supplied around the taper 305 and collar 306. As a result, the tapered portion 305 and the collar 306 are lifted from the bearings 307a and the bearings 307b, respectively, and the rotating shaft 303 rotates without causing friction with the bearings 307a and the bearings 307b. The pressure of the gas acts perpendicular to the tapered surface of the tapered portion 305 and the tapered surface of the collar 306, and the pressure of the gas acts not only in the radial direction but also in the thrust direction. For this reason, in the turbocharger 300, a thrust bearing is unnecessary.

  Patent Document 2 describes an air bearing device 500 including a rotating shaft 501, a bearing member 503, a bearing member 504, an air bearing 506, an air bearing 507, a flow passage 508, and a flow passage 509 as shown in FIG. It is done. The air bearing 506 is formed between the rotating shaft 501 and the bearing member 503. The air bearing 507 is formed between the rotating shaft 501 and the bearing member 504. A channel 508 is provided in the bearing member 503, and a channel 509 is provided in the bearing member 504. Pressurized air is supplied from the flow path 508 to the air bearing 506. In addition, pressurized air is supplied from the flow path 509 to the air bearing 507. The air bearing 506 and the air bearing 507 are formed in a tapered shape, and the large diameter side of the air bearing 506 and the large diameter side of the air bearing 507 face each other. In Patent Document 2, the positional relationship between the air bearing device 500 and the impeller to be attached to the rotating shaft 501 is not clear.

Japanese Patent Application Laid-Open No. 62-13816 Japanese Patent Application Laid-Open No. 58-196319

  According to the turbocharger 300 described in Patent Document 1, there is room for improvement in the vibration characteristics of the turbocharger 300 when the rotating shaft 303 rotates. Thus, the present disclosure provides a turbomachine having good vibration characteristics.

The present disclosure
A turbo machine for a refrigeration cycle apparatus using a refrigerant whose saturation vapor pressure at normal temperature is a negative pressure as a working fluid,
With the rotation axis,
A first impeller fixed to the rotating shaft and including a low pressure surface which receives a relatively low pressure by the working fluid as the rotating shaft rotates;
A first bearing disposed on the low pressure surface side of the first impeller and supporting the rotating shaft;
And a second bearing that supports the rotating shaft on the side opposite to the first bearing with the first impeller interposed therebetween.
The rotating shaft includes a first tapered portion having a diameter that expands toward the low pressure surface of the first impeller at least in the region supported by the first bearing,
The first bearing has a first support surface whose diameter increases toward the low pressure surface of the first impeller to support the first tapered portion.
The first bearing, the first impeller, and the second bearing are disposed in this order along the longitudinal direction of the rotation shaft.
Provide turbomachinery.

  The above turbomachine has good vibration characteristics.

Sectional view of a turbomachine according to an example of the first embodiment Sectional view of a turbomachine according to another example of the first embodiment Sectional view of a turbomachine according to an example of the second embodiment Sectional view of a turbomachine according to another example of the second embodiment Sectional drawing of the 1st taper part and the 1st bearing concerning the 1st modification Sectional drawing of the 2nd taper part and the 2nd bearing concerning the 1st modification Graph explaining the effect of the first modification Sectional drawing of the 1st taper part and the 1st bearing concerning the 2nd modification Sectional drawing of the 2nd taper part and the 2nd bearing concerning the 2nd modification Sectional drawing of the 1st taper part and the 1st bearing concerning the 3rd modification Sectional drawing of the 2nd taper part and the 2nd bearing concerning the 3rd modification Cross section showing a conventional turbocharger Cross-sectional view showing a conventional air bearing device

(Findings that formed the basis of this disclosure)
The present inventors use and discharge a working fluid whose saturated vapor pressure is a negative pressure (absolute pressure and lower than atmospheric pressure) at normal temperature (Japanese Industrial Standard: 20 ° C. ± 15 ° C./JIS Z 8703) We examined a turbomachine where the pressure of the working fluid was negative. As a result, the following findings were obtained.
In a refrigeration cycle apparatus using a refrigerant whose saturation vapor pressure at normal temperature is a negative pressure as a working fluid, compared to a refrigeration cycle apparatus using a refrigerant whose saturation vapor pressure at normal temperature is a positive pressure as a working fluid, It is required to realize a higher pressure ratio. Therefore, the turbomachine requires extremely high rotational speed as the rotational speed of the rotating body. Further, due to this, in the turbo machine, abnormal vibration due to resonance is likely to occur. The inventors of the present invention conducted intensive studies, and biased the mass distribution of the rotating body in the axial direction to a position close to the center of gravity and increased the bending natural frequency of the rotating body to obtain the bending natural frequency of the rotating body. It has been found that the rotational speed can be made higher than the rated rotational speed, thereby suppressing abnormal vibration due to resonance.
Based on the above findings, the present inventors have conceived of the invention of each aspect described below.

A turbomachine according to a first aspect of the present disclosure is
A turbo machine for a refrigeration cycle apparatus using a refrigerant whose saturation vapor pressure at normal temperature is a negative pressure as a working fluid,
With the rotation axis,
A first impeller fixed to the rotating shaft and including a low pressure surface which receives a relatively low pressure by the working fluid as the rotating shaft rotates;
A first bearing disposed on the low pressure surface side of the first impeller and supporting the rotating shaft;
And a second bearing that supports the rotating shaft on the side opposite to the first bearing with the first impeller interposed therebetween.
The rotating shaft includes a first tapered portion having a diameter that expands toward the low pressure surface of the first impeller at least in the region supported by the first bearing,
The first bearing has a first support surface whose diameter increases toward the low pressure surface of the first impeller to support the first tapered portion.
The first bearing, the first impeller, and the second bearing are disposed in this order along the longitudinal direction of the rotating shaft.

  According to the first aspect, the first bearing having the relatively large mass is sandwiched by the first bearing and the second bearing. For this reason, it is suppressed that the mass distribution of the rotating body including the rotation axis is biased to a position away from the center of gravity position. As a result, the bending natural frequency of the rotating body including the rotation axis is relatively high, and even if the rotation axis rotates at high speed, abnormal vibration due to resonance does not easily occur. As a result, the turbomachine according to the first aspect has good vibration characteristics.

  Further, according to the first aspect, the first bearing has a first support surface for supporting the first tapered portion, and the first bearing is disposed on the low pressure surface side of the first impeller. The diameter of the first taper increases towards the first impeller. Therefore, the rotation axis can be formed such that the cross-sectional area at the central portion of the rotation axis is relatively large. As a result, the bending natural frequency of the rotating body including the rotation axis is relatively high, and even if the rotation axis rotates at high speed, abnormal vibration due to resonance does not easily occur. Furthermore, according to the first aspect, since the first bearing is disposed on the low pressure surface side of the first impeller, the thrust load in the direction from the first impeller toward the first bearing can be supported by the first bearing.

Further, according to the first aspect, a refrigerant whose saturated vapor pressure at normal temperature is a negative pressure is used as the working fluid.
As described above, when a refrigerant whose saturated vapor pressure at normal temperature is a negative pressure is used as the working fluid, the turbo machine needs a high rotational speed as the rotational speed of the impeller. Further, due to this, in the turbo machine, abnormal vibration due to resonance is likely to occur. On the other hand, the turbomachine of the first aspect can suppress abnormal vibration due to resonance while using a refrigerant whose saturated vapor pressure at normal temperature is a negative pressure as the working fluid.
Furthermore, when a refrigerant whose saturated vapor pressure at normal temperature is a negative pressure is used as the working fluid, the thrust load generated is a turbo compressor even if the turbo machine is a high pressure ratio (for example, a pressure ratio of 2 or more) Very small. Therefore, according to the first aspect, it is possible to support the thrust load generated by the rotation by the first bearing (for example, the tapered slide bearing) having the first support surface for supporting the first tapered portion alone. Thus, the first aspect is superior to a turbomachine provided with thrust bearings and radial bearings separately, in that the device configuration is simple.

The first aspect of the present disclosure is superior to the turbocharger disclosed in Patent Document 1 in the following points.
According to the turbocharger 500 described in Patent Document 1, the diameter of the rotating shaft 303 is the narrowest at the central portion of the rotating shaft 303, and the compressor wheel 304 is attached to the tip of the rotating shaft 303. Therefore, the bending natural frequency of the rotating body including the rotating shaft 303 and the compressor wheel 304 is low, and abnormal vibration due to resonance may occur in the rotating shaft 303 when the rotating shaft 303 rotates at high speed.
On the other hand, according to the turbomachine of the present disclosure, as described above, the diameter of the first tapered portion is expanded toward the first impeller. Therefore, the rotation axis can be formed such that the cross-sectional area at the central portion of the rotation axis is relatively large. As a result, the bending natural frequency of the rotating body including the rotation axis is relatively high, and even if the rotation axis rotates at high speed, abnormal vibration due to resonance does not easily occur.
Furthermore, the turbocharger 500 disclosed in Patent Document 1 requires at least two divisions of the rotating shaft 303 or the casing due to its configuration. Therefore, it is predicted that this causes problems such as insufficient rigidity and generation of vibration. On the other hand, the turbomachine of the first aspect is excellent in that such a problem does not occur.

  In the second aspect of the present disclosure, for example, the turbomachine according to the first aspect further includes a second impeller fixed to the rotation shaft, the first bearing, the first impeller, and the second impeller And the second bearing may be disposed in this order along the longitudinal direction of the rotation shaft. According to the second aspect, when the turbomachine is, for example, a turbocompressor, the compression efficiency can be improved by the two-stage compression to achieve a high pressure ratio.

  In the third aspect of the present disclosure, for example, in the second impeller of the turbomachine according to the second aspect, the surface receiving a relatively low pressure by the working fluid when the rotation shaft rotates is the rotation shaft The second bearing may be closer to the second bearing than a surface that receives a relatively higher pressure by the working fluid as it rotates. According to the third aspect, since the thrust load generated by the first impeller and the thrust load generated by the second impeller are in opposite directions, these are offset. As a result, when the turbomachine is, for example, a turbocompressor, the range of operable pressure ratios is expanded.

  In a fourth aspect of the present disclosure, in the second impeller of the turbomachine according to the second aspect, the surface receiving a relatively high pressure by the working fluid when the rotation shaft rotates has the rotation shaft rotated. The second bearing may be closer to the second bearing than a surface which receives a relatively lower pressure by the working fluid. According to the fourth aspect, the flow path of the working fluid between the first impeller and the second impeller is shortened, and the turbomachine can be miniaturized.

  In a fifth aspect of the present disclosure, the inclination angle of the first support surface with respect to the central axis of the tapered hole formed by the first support surface of the turbomachine according to any one of the first to fourth aspects is: The inclination angle of the first tapered portion with respect to the central axis of the rotation axis may be larger. According to the fifth aspect, the pressure applied to the lubricant between the first support surface and the first tapered portion can be prevented from being dispersed in the axial direction of the rotation shaft. Therefore, it is possible to prevent the spatial variation of the bearing load and to increase the bearing load capacity.

  In a sixth aspect of the present disclosure, the first bearing according to any one of the first to fifth aspects has a first supply hole for supplying a lubricant to the first support surface. It may be According to the sixth aspect, the lubricant can be supplied to the first support surface, and seizure due to exhaustion of the lubricant can be prevented.

  In a seventh aspect of the present disclosure, the first feed hole of the turbomachine according to the sixth aspect is an end where the diameter of the first tapered portion is smaller than the end where the diameter of the first tapered portion is the largest. It may be provided at a position close to the unit. According to the seventh aspect, the static pressure effect by the lubricant can be given preferentially to the small diameter side of the first tapered portion where the pressure of the lubricant is relatively small. This increases the bearing load capacity of the entire first bearing.

  In an eighth aspect of the present disclosure, the first bearing of the turbomachine according to the sixth aspect or the seventh aspect includes the first porous member forming all or a part of the first support surface. Good. According to the eighth aspect, in the first bearing, spatial variations in temperature or pressure of the lubricant can be suppressed.

  In a ninth aspect of the present disclosure, when the rotation axis of the turbomachine according to any one of the first to eighth aspects extends in a gravity direction, and the rotation axis of the first impeller rotates. The surface receiving a relatively lower pressure by the working fluid may be located higher in the direction of gravity than the surface receiving a relatively higher pressure by the working fluid when the rotation shaft rotates. . According to the ninth aspect, the thrust load generated by the rotation of the rotation shaft can be offset by the gravity acting on the rotating body including the rotation shaft. As a result, when the turbomachine is, for example, a turbocompressor, the range of operable pressure ratios is expanded.

  In a tenth aspect of the present disclosure, a second of the turbomachine according to any one of the first to ninth aspects, having a diameter increasing toward the first impeller at a position corresponding to the second bearing of the turbomachine The second bearing may have a tapered portion, and the second bearing may have a second support surface whose diameter increases toward the first impeller to support the second tapered portion. According to the tenth aspect, the second bearing can support the thrust load in the opposite direction to the direction from the first impeller to the first bearing.

  In an eleventh aspect of the present disclosure, the tilt angle of the second support surface with respect to the central axis of the tapered hole formed by the second support surface of the turbomachine according to the tenth aspect is the second angle with respect to the central axis of the rotation axis. It may be larger than the inclination angle of the tapered portion. According to the eleventh aspect, it is possible to prevent the pressure applied to the lubricant between the second support surface and the second tapered portion from being dispersed in the axial direction of the rotation shaft. Therefore, it is possible to prevent the spatial variation of the bearing load and to increase the bearing load capacity.

  In a twelfth aspect of the present disclosure, the second bearing of the turbomachine according to the tenth aspect or the eleventh aspect may have a second supply hole for supplying a lubricant to the second support surface. According to the twelfth aspect, the lubricant can be supplied to the second support surface, and seizure due to exhaustion of the lubricant can be prevented.

  In a thirteenth aspect of the present disclosure, the second supply hole of the turbomachine according to the twelfth aspect is an end where the diameter of the second tapered portion is smaller than the end where the diameter of the second tapered portion is the largest. It may be provided at a position close to the unit. According to the thirteenth aspect, the static pressure effect of the lubricant can be preferentially imparted to the small diameter side of the second tapered portion where the pressure of the lubricant is relatively small. This increases the bearing load capacity of the entire second bearing.

  In a fourteenth aspect of the present disclosure, the second bearing of the turbomachine according to the twelfth aspect or the thirteenth aspect includes the second porous member forming all or a part of the second support surface. Good. According to the fourteenth aspect, spatial variations in the temperature or pressure of the lubricant can be suppressed in the second bearing.

A turbomachine according to a fifteenth aspect of the present disclosure is
A turbo machine for a refrigeration cycle apparatus using a refrigerant whose saturated vapor pressure at normal temperature is a negative pressure,
With the rotation axis,
It has a low pressure surface which receives a relatively low pressure by the working fluid when the rotary shaft rotates, and a high pressure surface which faces the low pressure surface, and the force generated by the pressure difference between the low pressure surface and the high pressure surface is the high pressure A first impeller generated from the surface toward the low pressure surface;
A first bearing that supports the rotating shaft on the low pressure surface side of the first impeller;
The center of gravity of the rotating body including the first impeller and the rotation axis is located on the high pressure side of the first impeller,
The rotating shaft has a first tapered portion with a diameter that expands toward the low pressure surface of the first impeller on the low pressure surface side of the first impeller.
The first bearing supports the first tapered portion and has a first support surface of a diameter that increases toward the low pressure surface of the first impeller.

  Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The following description relates to an example of the present disclosure, and the present disclosure is not limited thereto.

First Embodiment
As shown in FIG. 1, the turbomachine 100 a includes a rotating shaft 4, a first impeller 3 a, a first bearing 1, and a second bearing 2. The turbo machine 100a is, for example, a turbo compressor. The first impeller 3 a is fixed to the rotation shaft 4. The first impeller 3 a also includes a low pressure surface 31. The low pressure surface 31 is a surface which receives relatively low pressure by the working fluid when the rotary shaft 4 rotates, of both the axial direction of the first impeller 3a. The first bearing 1 is disposed on the low pressure surface 31 side of the first impeller 3a. The first bearing 1 is a bearing for supporting the rotating shaft 4. The first bearing 1 supports the vicinity of the tip of the rotary shaft 4 on the side to which the working fluid of the first impeller 3 a is supplied. The second bearing 2 is arranged to sandwich the first impeller 3 a together with the first bearing 1. The second bearing 2 is a bearing for supporting the rotating shaft 4. The second bearing 2 is disposed on the opposite side of the low pressure surface 31 of the first impeller 3a. The rotation shaft 4 includes a first tapered portion 41 having a diameter that expands toward the first impeller 3a. The first tapered portion 41 is formed on the low pressure surface 31 side of the first impeller 3a. The first bearing 1 has a first support surface 11 for supporting the first tapered portion 41.

  Turbo machine 100 a further includes a casing 5 and a motor 6. The first impeller 3 a and the motor 6 are connected by the rotating shaft 4. The second bearing 2 is disposed at a position farther from the first impeller 3 a than the motor 6. A discharge passage 71 is formed by the casing 5 on the outer peripheral side of the first impeller 3a. By driving the motor 6, the first impeller 3a is rotated at high speed along with the rotation shaft 4. Thus, the working fluid flows from the front of the first impeller 3a (left side of the first impeller 3a in FIG. 1) toward the first impeller 3a. The working fluid is accelerated and pressurized by the rotating first impeller 3 a and discharged from the turbomachine 100 a through the discharge passage 71. At this time, the left surface of the first impeller 3a in FIG. 1 receives the suction pressure of the working fluid, and the right surface of the first impeller 3a receives a pressure substantially equal to the discharge pressure of the working fluid. That is, the low pressure surface 31 receives relatively low pressure by the working fluid when the rotating shaft 4 rotates. Therefore, a differential pressure is generated on both sides in the axial direction of the first impeller 3a, and this differential pressure generates a thrust load in the left direction of FIG. 1 on the rotating body including the rotating shaft 4 and the first impeller 3a. . The first bearing 1 is configured as, for example, a slide bearing, and a lubricant is included between the first support surface 11 and the first tapered portion 41. The first support surface 11 forms a tapered hole having a diameter slightly larger than that of the first tapered portion 41. That is, a tapered hole whose diameter is enlarged toward the first impeller 3 a is formed by the first support surface 11. Thereby, the generated thrust load is supported.

  In the turbo machine 100a, the first impeller 3a having a relatively large mass is sandwiched between the first bearing 1 and the second bearing 2. For this reason, it is suppressed that the mass distribution of the rotating body including the rotating shaft 4 and the first impeller 3a is biased to a position far away from the center of gravity position, and the reduction of the bending natural frequency of the rotating body is suppressed. Thereby, the bending natural frequency of the rotating body including the rotating shaft 4 and the first impeller 3a can be sufficiently higher than the rotation speed of the rotating body. For this reason, since the rotation speed of the rotating body and the bending natural frequency of the rotating body are not close to each other, abnormal vibration due to resonance does not easily occur even if the rotating shaft 4 rotates at high speed. As a result, the turbomachine 100a has good vibration characteristics.

  The bending natural frequency of the rotating body increases as the cross-sectional area of the rotating shaft increases, and in particular, the cross-sectional area of the central portion of the rotating shaft corresponding to "antinode" in the primary bending mode of vibration is the most suitable for the bending natural frequency of the rotating body. It greatly affects. The first bearing 1 has a first support surface 11 for supporting the first tapered portion 41, and the first bearing 1 is disposed on the low pressure surface 31 side of the first impeller 3a. The diameter of the first tapered portion 41 is expanded toward the first impeller 3a. For this reason, the rotation shaft 4 can be formed so that the cross-sectional area in the center part of the rotation shaft 4 becomes comparatively large. As a result, the bending natural frequency of the rotating body including the rotating shaft 4 and the first impeller 3a is relatively high, and even if the rotating shaft 4 rotates at high speed, abnormal vibration due to resonance does not easily occur. As a result, the turbomachine 100a has good vibration characteristics.

  The rotating shaft 4 and the second bearing 2 may be configured as shown in FIG. The turbomachine 100b is configured the same as the turbomachine 100a except that the rotating shaft 4 and the second bearing 2 are configured as shown in FIG. In the turbo machine 100b, the rotating shaft 4 includes a second tapered portion 42. The second tapered portion 42 has a diameter increasing toward the first impeller 3a. The second bearing 2 also has a second support surface 21 for supporting the second tapered portion 42. The second bearing 2 is configured, for example, as a slide bearing. The second support surface 21 forms a tapered hole having a diameter slightly larger than that of the second tapered portion 42. A lubricant is contained between the second support surface 21 and the second tapered portion 42.

  When the rotating body including the rotating shaft 4 and the first impeller 3a rotates at high speed, vibrational load may occur due to imbalance of mass characteristics of the rotating body or asymmetric fluid force of the working fluid. If the axial load of this vibrational load is large, the thrust load of the rotating body including the rotating shaft 4 and the first impeller 3a may be applied in the direction opposite to the direction from the first impeller 3a toward the first bearing 1 . Such a thrust load can be supported by the second bearing 2.

  In the turbo machine 100b, the second bearing 2 is arranged between the first bearing 1 and the second bearing 2 so that the axial center of the rotating shaft 4 is located. Thereby, it can prevent that the cross-sectional area of the center part of the rotating shaft 4 becomes small. In addition, even if the rotating shaft 4 is connected to another rotating shaft by, for example, a universal joint, the bending vibration of the rotating body including the rotating shaft 4 is hardly affected by the other rotating shaft. For this reason, in this case, the axial center of the rotation shaft 4 is determined without regard to another rotation shaft connected to the rotation shaft 4.

Second Embodiment
Next, a turbomachine 100c and a turbomachine 100d according to a second embodiment will be described. The turbomachine 100c and the turbomachine 100d according to the second embodiment are configured in the same manner as the turbomachine 100a except in the case where they are particularly described. The components of the turbomachine 100c that are the same as or correspond to those of the turbomachine 100a may be denoted by the same reference numerals as those of the turbomachine 100a, and the detailed description thereof may be omitted. The description of the first embodiment applies to the present embodiment as long as there is no technical contradiction.

  The turbomachine 100c further includes a second impeller 3b. The second impeller 3 b is fixed to the rotation shaft 4. The first bearing 1 and the second bearing 2 are disposed to sandwich the first impeller 3a and the second impeller 3b. Here, the second bearing 2 is configured in the same manner as the second bearing 2 of the turbomachine 100b, and along with this, the rotary shaft 4 includes a second tapered portion 42. The second impeller 3 b includes a low pressure surface 131 and a high pressure surface 132. The low pressure surface 131 is a surface of the second impeller 3b which receives a relatively low pressure by the working fluid when the rotating shaft 4 rotates. The high pressure surface 132 is the surface opposite to the low pressure surface 131. A discharge passage 73 is formed by the casing 5 on the outer peripheral side of the second impeller 3b. In addition, the turbo machine 100c includes a connection flow path 72 that brings the discharge flow path 71 into communication with the space on the low pressure surface 131 side of the second impeller 3b. The turbo machine 100c is, for example, a turbo compressor. The working fluid pressurized by the first impeller 3a is sucked into the second impeller 3b through the discharge flow channel 71 and the connection flow channel 72. The working fluid is accelerated and pressurized by the rotating second impeller 3 b and discharged from the turbomachine 100 c through the discharge flow path 73. As described above, since the working fluid is compressed in two stages by the first impeller 3a and the second impeller 3b, the compression efficiency is improved and a high pressure ratio can be achieved.

  The second impeller 3b is fixed to the rotation shaft 4 so that the surface (high pressure surface 132) opposite to the low pressure surface 131 faces the first impeller 3a. When the second impeller 3b is rotated, the right surface of the second impeller 3b in FIG. 3 receives the suction pressure of the working fluid, and the left surface of the first impeller 3a has a pressure substantially equal to the discharge pressure of the working fluid. receive. Therefore, the thrust load in the right direction of FIG. 3 is generated by the rotation of the second impeller 3b. That is, the direction of the thrust load generated by the rotation of the first impeller 3a is opposite to the direction of the thrust load generated by the rotation of the second impeller 3b. For this reason, since these thrust loads cancel each other, the range of the operable pressure ratio of the turbomachine 100c is wide.

  Like the turbomachine 100d shown in FIG. 4, the second impeller 3b may be fixed to the rotation shaft 4 so that the low pressure surface 131 faces the first impeller 3a. In this case, the flow path (connection flow path 72) of the working fluid between the first impeller 3a and the second impeller 3b can be shortened. Thus, the turbomachine 100d is miniaturized as compared with the turbomachine 100c.

<Modification>
The turbo machine 100a and the turbo machine 100b according to the first embodiment and the turbo machine 100c and the turbo machine 100d according to the second embodiment can be modified from various viewpoints. Hereinafter, modified examples of the turbo machines 100a to 100d will be described. Note that among the components according to the following modification, components that are the same as or correspond to those of the turbo machines 100a to 100d are given the same reference numerals, and detailed descriptions thereof may be omitted.

(First modification)
The support surface 11 of the first bearing 1 and the support surface 21 of the second bearing 2 may be formed as shown in FIGS. 5A and 5B, respectively. In the first support surface 11, the inclination angle θ ₂ of the first support surface 11 with respect to the central axis Q 1 of the tapered hole formed by the first support surface 11 is the inclination angle of the first tapered portion 41 with respect to the central axis P of the rotation shaft 4. and it is formed to be greater than theta _1. Further, in the second support surface 21, the inclination angle θ ₄ of the second support surface 21 with respect to the central axis line Q 2 of the tapered hole formed by the second support surface 21 has a second tapered portion 42 with respect to the central axis P of the rotation shaft 4. and it is formed to be greater than the inclination angle theta _3. In this case, the ratio (θ ₂ / θ ₁ ) of the inclination angle θ _{2 to} the inclination angle θ ₁ is, for example, 1.0001 to 1.01. Further, the ratio (θ ₄ / θ ₃ ) of the inclination angle θ _{4 to} the inclination angle θ ₃ is, for example, 1.0001 to 1.01.

The state of lubrication between the bearing and the shaft being lubricated by the lubricant can be evaluated by the following Sommerfeld numbers. Here, μ is the viscosity coefficient [Pa · s] of the lubricant, N is the rotational speed of the shaft [s ^-1 ], P is the load surface pressure (load load / meridional section area) [Pa], R Denotes the radius [m] of the shaft, and c denotes the radial gap [m] between the bearing and the shaft.
Sommerfeld number = (μN / P) × (R / c) ²

In FIG. 6, the pressure of the lubricant between the first support surface 11 and the first taper portion 41 and the minimum diameter of the first support surface 11 at which the hole diameter of the tapered hole formed by the first support surface 11 is minimized. The relationship with the distance from the end to the axial direction is shown. The lower the Sommerfeld number, the lower the pressure on the lubricant. Since the radius of the large diameter portion of the first tapered portion 41 is larger than the radius of the small diameter portion of the first tapered portion 41, the inclination angle theta ₁ and the inclination angle theta ₂ are equal, the pressure of the lubricant is shown in dashed lines in FIG. 6 As described above, the diameter of the first tapered portion 41 becomes higher on the large diameter side. For this reason, the bearing load is biased to the large diameter side of the first tapered portion 41. In contrast, as described above, if the relation is defined between the inclination angle theta ₁ and the inclination angle theta _2, the variation of the Sommerfeld number is reduced in the axial direction of the first tapered portion 41. For this reason, the variation in the pressure distribution of the lubricant in the axial direction of the first tapered portion 41 is reduced as shown by the solid line in FIG. Thereby, bearing load capacity can be increased. This also applies to the relationship between the inclination angle theta ₃ the inclination angle theta _4.

  A virtual intersection obtained by extending the ridge line of the first support surface 11 when the first bearing 1 is cut along the central axis Q1 is defined as the intersection 1. Further, a virtual intersection obtained by extending the ridge line of the first tapered portion 41 when the first tapered portion 41 is cut along the central axis P is defined as the intersection 2. In order to reduce variation in the number of sommer felts in the axial direction of the first tapered portion 41, it is desirable that the first support surface 11 be formed so that the intersection point 1 and the intersection point 2 coincide with each other. This applies to the relationship between the second support surface 21 and the second tapered portion 42.

(2nd modification)
As shown in FIG. 7A, the first bearing 1 may have a first supply hole 12 for supplying a lubricant to the first support surface 11. Thereby, the lubricant can be supplied to the first support surface 11, and the burn-in due to the exhaustion of the lubricant can be prevented. Also, the high pressure lubricant is supplied through the first supply hole 12 to obtain supporting force of the rotating body including the rotating shaft 4 by the static pressure effect. Not only the supporting force by the dynamic pressure effect generated by the rotation of the rotating shaft 4 but also the supporting force by the static pressure effect is applied, the rotating shaft 4 can be lifted even when the rotating shaft 4 is stopped. As a result, when the rotation of the rotary shaft 4 stops, it is possible to suppress wear of the sliding surfaces of the first bearing 1 and the rotary shaft 4 to a very low level. Since the bearing force due to the static pressure effect acts on the first bearing surface 11 perpendicularly, it has not only a radial bearing component but also an axial bearing component. For this reason, the bearing load capacity in the axial direction can be increased.

  Further, as shown in FIG. 7A, it is desirable that the first supply hole 12 be closer to the end where the diameter of the first tapered portion 41 is the smallest than the end where the diameter of the first tapered portion 41 is the largest. Thereby, the static pressure effect by the lubricant can be given preferentially to the small diameter side of the first tapered portion 41 in which the pressure of the lubricant is relatively small. As a result, the bearing load capacity of the entire first bearing 1 is increased.

  As shown in FIG. 7B, the second bearing 2 may have a second supply hole 22 for supplying a lubricant to the second support surface 21. Further, it is desirable that the second supply hole 22 be closer to the end where the diameter of the second tapered portion 42 is the smallest than the end where the diameter of the second tapered portion 42 is the largest. Thereby, also in the second bearing 2, the above-mentioned effect is obtained.

(Third modification)
As shown in FIG. 8A, in addition to having the first supply holes 12, the first bearing 1 is provided with the first porous member 13 forming all or part of the first support surface 11. It may be Moreover, as shown to FIG. 8B, in addition to having the 2nd supply hole 22, the 2nd bearing 2 forms the 2nd porous member 23 which forms all or one part of the 2nd support surface 21. May be provided. The first porous member 13 and the second porous member 23 are made of, for example, a porous material such as sintered metal, growth cast iron, or synthetic resin. If the number of the first supply holes 12 is one or a few, the temperature or pressure of the lubricant in the vicinity of the first supply holes 12 and the temperature or pressure of the lubricant at a position away from the first supply holes 12 It may be different. Thereby, the rotation of the rotating shaft 4 may become unstable. This is also true when the number of second feed holes 22 is one or a few. When all or part of the first support surface 11 is formed by the first porous member 13, spatial variations in temperature or pressure of the lubricant can be suppressed in the first bearing 1. In addition, when all or part of the second support surface 21 is formed by the second porous member 23, in the second bearing 2, spatial variations in the temperature or pressure of the lubricant can be suppressed.

(Other modifications)
The rotation axis 4 may extend in the horizontal direction or in the vertical direction. When the rotating shaft 4 extends in the vertical direction, the first impeller 3a is fixed to the rotating shaft 4 so that the thrust load generated by the rotation of the rotating shaft 4 acts in the opposite direction to the vertical direction. desirable. In this case, the thrust load generated by the rotation of the rotating shaft 4 can be offset by the gravity acting on the rotating body including the rotating shaft 4 and the first impeller 3a. This widens the range of operable pressure ratios of the turbomachine.

  The present disclosure is useful for a compressor of a refrigeration cycle apparatus that can be used for air conditioning products such as turbo chillers and commercial air conditioning.

1 first bearing 2 second bearing 3a first impeller 3b second impeller 4 rotary shaft 11 first support surface 12 first supply hole 13 first porous member 21 second support surface 22 second supply hole 23 second supply hole Two porous members 31 low pressure surface 41 first tapered portion 42 second tapered portion 100a to 100d turbomachine

Claims (14)

A turbo machine for a refrigeration cycle apparatus using a refrigerant whose saturation vapor pressure at normal temperature is a negative pressure as a working fluid,
With the rotation axis,
A first impeller fixed to the rotating shaft and including a low pressure surface which receives a relatively low pressure by the working fluid as the rotating shaft rotates;
A first bearing disposed on the low pressure surface side of the first impeller and supporting the rotating shaft;
And a second bearing that supports the rotating shaft on the side opposite to the first bearing with the first impeller interposed therebetween.
The rotating shaft includes a first tapered portion having a diameter that expands toward the low pressure surface of the first impeller at least in the region supported by the first bearing,
The first bearing has a first support surface whose diameter increases toward the low pressure surface of the first impeller to support the first tapered portion.
The first bearing, the first impeller, and the second bearing are disposed in this order along the longitudinal direction of the rotation shaft.
Turbo machine. It further comprises a second impeller fixed to the rotating shaft,
The turbo machine according to claim 1, wherein the first bearing, the first impeller, the second impeller, and the second bearing are disposed in this order along the longitudinal direction of the rotation shaft.   The surface of the second impeller, which receives a relatively lower pressure by the working fluid when the rotation shaft rotates, is a surface that receives a relatively higher pressure by the working fluid when the rotation shaft rotates. The turbo machine according to claim 2, wherein the second bearing is also close to the second bearing.   The surface of the second impeller, which receives a relatively higher pressure by the working fluid when the rotation shaft rotates, is a surface that receives a relatively lower pressure by the working fluid when the rotation shaft rotates. The turbo machine according to claim 2, wherein the second bearing is also close to the second bearing.   The inclination angle of the first support surface with respect to the central axis of the tapered hole formed by the first support surface is larger than the inclination angle of the first tapered portion with respect to the central axis of the rotation axis. The turbo machine according to any one of the items.   The turbo machine according to any one of claims 1 to 5, wherein the first bearing has a first supply hole and supplies a lubricant to the first support surface via the first supply hole.   The first supply hole is provided at a position closer to an end where the diameter of the first tapered portion is the smallest than an end where the diameter of the first tapered portion is the largest. Turbo machine.   The turbo machine according to claim 6, wherein the first bearing comprises a first porous member forming all or part of the first support surface. The rotation axis extends in the direction of gravity,
The surface of the first impeller that receives a relatively lower pressure by the working fluid when the rotating shaft rotates is a surface that receives a relatively higher pressure by the working fluid when the rotating shaft rotates. The turbo machine according to any one of claims 1 to 8, wherein the turbo machine is also located upward in the direction of gravity. The rotating shaft has a second tapered portion having a diameter increasing toward the first impeller at a position corresponding to the second bearing,
The turbomachine according to any one of claims 1 to 9, wherein the second bearing has a second support surface whose diameter increases toward the first impeller to support the second tapered portion. .   The turbo according to claim 10, wherein the inclination angle of the second support surface with respect to the central axis of the tapered hole formed by the second support surface is larger than the inclination angle of the second tapered portion with respect to the central axis of the rotation axis. machine.   The turbo machine according to claim 10, wherein the second bearing has a second supply hole and supplies a lubricant to the second support surface via the second supply hole.   The second supply hole according to claim 12, wherein the second supply hole is provided at a position closer to the end at which the diameter of the second tapered portion is the smallest than the end at which the diameter of the second tapered portion is the largest. Turbo machine.   The turbo machine according to claim 12, wherein the second bearing comprises a second porous member forming all or part of the second support surface.

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